Rebody Replica veglia speedo gauge. A couple of questions..

[Pond]

I have a question for anyone who has fitted the ETB replica Veglia gauges to their car.
Did you run new wires from the speed sensor on the diff to the speedo speed signal input?
Or did you use the existing BMW wires either from the diff output (red/brown and brown/black earth), or the BMW cluster output (black/white) on connector X271?

I ask because I have a problem with my speedo. I used the black/white wire from the output speed signal on the BMW cluster PCB which worked fine until last week. Now the speedo has gone AWOL. I have re-wired the signal cable to the red/brown BMW input cable from the diff and earthed the other diff wire. This has made little difference; my speedo goes nuts every time the car moves!

The manufacturer is adamant it can't be a fault with the speedo; it must be my wiring is picking up 'noise' and causing the speedo to go nuts. I am not convinced but need to eliminate this before I send the unit back for diagnosis.

BTW I originally wired into input 3 (red and blue) on the speedo, not the yellow input 2. I have kept it on the red/blue with the new wire as this is correct for the type of signal. I think I should have originally wired into the yellow on the speedo (input 2) with the original wire, but it all worked absolutely fine.

Thanks.

 

[Pingu]

This is my wiring diagram for the Speedometer. I've used BMW's symbols and wiring colour rules, but page numbers agree with my wiring diagram, not those of standard Z3s.

https://www.porterbility.co.uk/Kit_Car_Build_files/Wiring_Diagrams/6211.0-01_03.pdf

Ignore the circuit inside the big box - it is wrong, but the connection numbers and wiring colours are correct.

 

[Pond]

This is my wiring diagram for the Speedometer. I've used BMW's symbols and wiring colour rules, but page numbers agree with my wiring diagram, not those of standard Z3s.

https://www.porterbility.co.uk/Kit_Car_Build_files/Wiring_Diagrams/6211.0-01_03.pdf

Ignore the circuit inside the big box - it is wrong, but the connection numbers and wiring colours are correct.

I have your wiring diagrams from before, thanks.
It is not so much "how" it is wired (as I know mine is correct), it's more about where the cables run and if they are the original BMW, or if they have been replaced, ideally with shielded cable.
As I said above, I am being told I have "noise" interfering with my speed signal from other cables within the loom.
However, I can't see where this "noise" has suddenly come from, as the speedo worked absolutely fine for months. My wires are the original red/brown and black/brown from the speed sensor directly to the speedo on input 2 (red/blue). I have earthed the black/brown directly to the car on a separate post so as not to get any interference from anywhere through the earth cable.

I have removed the speed sensor connector on the diff and cleaned it (although it looked fine). I have tested both cables running from the sensor into the car. Both have good continuity, so I know my cables are fine.

It still goes nuts whenever the car moves. I am 95% sure there is a problem with the speedo itself, but am being told it is almost impossible and must be my wiring.

 

[Pingu]

You could buy a cheap oscilloscope. Mine cost less that £20, and it's quite good.

Connect both wires from the diff to the 'scope. You should get a clean square wave. Noise would be "flutter" on the square wave.

Then reconnect the earth to the original position, and test again with the diff +ve wire and a wire from the 'scope to the same earth you are using for the speedo. Just a thought - have you checked the earth for the speedo?

 

[Pond]

Just a thought - have you checked the earth for the speedo?

Everything else works as it should. The earth to the speedo is common to all the gauges and all work fine. The speedo warning lights work, the odometer lights up, the backlight all works. The speedo powers up fine, just doesn't like the speed signal coming in for whatever reason (I am still convinced it is the instrument at fault not my wiring). Unless the speed sensor in the diff is playing up, which is highly unlikely, as it was all OK before the car was stored for the winter.

My hunch (and it is a guess) is that moisture has got into the gubbins of the speedo and is causing a fault. The ONLY thing that has changed by being in my garage for two months is condensation. All the external wiring connections are good with no issues.

 

[Pingu]

I agree and think it is your speedo that is playing up, but...

The earth wire is doubling up as a voltage wire for all the lights you talked about, and as a signal wire for the speedo. Signal wires are notorious for noise, but if it worked before, it should work now.

Does the speedo jump about when the wheels aren't moving, or only when they do?

A test I've done in the past is to disconnect the driveshafts and "drive the car". I was able to test the speedo and the diff sensor properly...

 

[Pond]

Does the speedo jump about when the wheels aren't moving, or only when they do?

It did initially when I earthed the sensor to a shared earth (with the fuel sensor). I then removed that and earthed it directly onto an unused earth post. That stopped it from jumping about just by switching the ignition on.
Now it behaves OK when I drive up to around 20mph, then it just goes nuts. It registered 535mph on the odometer computer and I was in my cul-de-sac!

It's worth mentioning that this all started when the speed sensor wire into the speedo was wired from the speed output from the BMW cluster.

I have since changed the wiring (to try and resolve the issue) to the input from the speed sensor and earthed it separately. Before it was only erthed through the existing earth via the BMW cluster.

Whatever I do, it makes no difference in reality. Which is why the manufacturer believes it is external 'noise' causing the issue. I just don't see it, as whatever 'noise' is around, it was there from when I first wired the car and it worked fine for months.

 

[Pingu]

Daft question, but did you change the port on the speedo head when you changed the speed signal source?

It's Pin 2 for ECU input, and Pin 3 for diff input.

 

[Pingu]

Something else you could consider is resetting the pulse counter.

I would accurately measure several tyre revolutions to find the tyre circumference.

Assuming revolution is measured in metres...

According to Google (which is never wrong ), there are 9 pulses per tyre revolution, so Distance per pulse = Circumference / 9

Pulse Count per mile = 1608 / ( Distance per pulse )

 

[Pond]

Something else you could consider is resetting the pulse counter.

I would accurately measure several tyre revolutions to find the tyre circumference.

Assuming revolution is measured in metres...

According to Google (which is never wrong ), there are 9 pulses per tyre revolution, so Distance per pulse = Circumference / 9

Pulse Count per mile = 1608 / ( Distance per pulse )

My pulses were set accurately before at 9 pulses x rear tyre circumference rotations in one mile. It is approximately 7500 pulses per mile with my wheels and tyres. I have cross-referenced this and know it's pretty accurate.
I have now changed the pulses (just in case there was a glitch) to just under 7000 for now to see if it makes a difference. If it works (which I doubt), then I shall change the pulses back to very near where it was.

 

[Pond]

Anyway, details aside, did you (@Pingu) run new wires from your speed sensor, or did you re-use the ones in the BMW loom (red/brown and black/brown)?

That is the important info I need.

 

[Pingu]

BMW (BR/RT) wire to a block, and the speedo head wire (RT/BL) from the block to the speedo head (Pin 3)

BMW (BR/SW) wire to an earth point. I think it is the one near the RH door.

 

[Pond]

BMW (BR/RT) wire to a block, and the speedo head wire (RT/BL) from the block to the speedo head (Pin 3)

BMW (BR/SW) wire to an earth point. I think it is the one near the RH door.

OK thanks. That is EXACTLY how I have it wired, yet I am still having problems with the needle going nuts.
The manufacturer is convinced it is 'noise' coming from elsewhere affecting the BMW signal wire (brown/red). I just don't see how, or why.
I am now leaning toward a fault inside the speedo causing it's own 'noise'.

I shall give it one more try on the road, then the speedo is coming out (again) and being sent back for diagnosis. Removing the dash enough to get the speedo out is a complete PITA, so I don't want to do that more than I absolutely have to.